The invention relates to a method for processing a traffic channel request in a cellular radio system in which a request is received for the allocation of a traffic channel to a mobile station from a particular radio cell. The invention further relates to a cellular radio system comprising at least a first and a second base station located close to each other and having traffic channels that utilize at least to some extent the same frequency channels, and allocation means for allocating a traffic channel to a mobile station from the first base station in response to a traffic channel request. The invention also relates to a base station controller comprising means for controlling base stations and allocation means for allocating a traffic channel to a mobile station from a particular radio cell in response to a traffic channel request received by the base station controller.
The invention relates to the allocation of a traffic channel to a mobile station of a cellular radio system in which a plurality of base stations utilize the same frequency channels in their traffic connections. In these systems, base stations using the same frequency channels may occasionally disturb each other, which degrades the quality of the connections transmitted through the base stations.
In known mobile communication systems the allocation of a traffic channel to a particular mobile station usually depends on whether or not there is a traffic channel available in a radio cell at a particular moment. In other words, if the radio cell concerned has a traffic channel available, it is allocated to a mobile station when needed. In the GSM system (Global System for Mobile Communications), for example, traffic channels are allocated as described above. Since the GSM system is time-divisional, a traffic channel to be allocated to a mobile station in the system consists of a time slot on a particular frequency channel. Alternatively, if frequency hopping is used, the frequency channel of the traffic channel changes from one time slot to another according to a predetermined frequency hopping sequence. The mobile station thus transmits alternately on all frequency channels included in the frequency hopping sequence.
A problem with the allocation of traffic channels in known mobile systems is that when a traffic channel is being allocated in a particular radio cell, the situation prevailing in adjacent cells in not taken into account in any way. Yet in practice the allocation of new traffic channels always affects to some extent at least the situation in the adjacent cells that utilize at least to some extent the same frequency channels.
An object of the present invention is to solve the above mentioned problem and to provide a method for allocating traffic channels which allows the quality of the traffic connections provided by the system to be maintained as high as possible. This is achieved with a method of the invention in which a request is received for the allocation of a traffic channel to a mobile station, the method being characterized in that the method comprises the steps of: calculating the number of traffic channels in use in said radio cell; measuring the quality of ongoing connections of adjacent radio cells using at least to some extent the same frequency channels as said radio cell; and deciding whether a traffic channel is to be allocated or not allocated, the number of traffic channels in use and the quality of the ongoing connections of the adjacent cells being at least taken into account in the decision so that the allocation of the traffic channel to the mobile station from said radio cell is prevented if the number of traffic channels in use exceeds a predetermined threshold value and if the mean value of quality for the ongoing connections of any of the adjacent cells is lower than a predetermined minimum quality value.
The invention is based on the idea that when a decision regarding the allocation of a traffic channel is made, also the situation prevailing in adjacent cells that employ, at least to some extent, the same frequency channels as the cell in which the new traffic channel is to be allocated is taken into account, thereby avoiding a situation where interference caused in the cells by the allocation of the new traffic channel rises to a level that degrades the quality of ongoing connections. In other words, even if the radio cell the received traffic channel request concerns would have a traffic channel available, the traffic channel is not automatically allocated to the mobile station. Instead, a mean value of quality is calculated for each adjacent cell, the value providing a mean value for the cell""s ongoing connections. If the mean value of quality for any of the cells is then discovered to be lower than a predetermined minimum quality value, or if the mean value of quality for the cells concerned can be assumed to decrease distinctly if a new traffic channel is allocated, the new traffic channel is not allocated. In this context xe2x80x98adjacent cellxe2x80x99 refers to a cell which is located so close to a cell in which a traffic channel is to be allocated that the new traffic channel can be assumed to affect the ongoing connections of the adjacent cell. The adjacent cell therefore need not be necessarily located next to the cell in which the traffic channel is to be allocated, but there can be another radio cell or several cells between the cells concerned.
In a preferred embodiment of the method of the invention the mobile station to which a channel is to be allocated is checked to find out whether the mobile station already has a traffic channel in use. This is taken into account when the decision concerning the allocation of the traffic channel is made; if the mobile station has a traffic channel in use and it abandons the channel in connection with the allocation of the new channel without thereby increasing interference in the system, the new traffic channel can be allocated to the mobile station (provided that a traffic channel is available), without taking into account the quality of the ongoing connections of the adjacent cells.
The invention further relates to a cellular radio system in which the method of the invention can be utilized. The cellular radio system of the invention is characterized in that the cellular radio system further comprises: means for finding out the number of traffic channels in use at the first base station; means for finding out a mean value of quality for ongoing traffic connections of said at least second base station; and comparison means for comparing the number of the traffic channels with a predetermined maximum number and for comparing the mean value of quality with a predetermined minimum quality value; and that said allocation means are responsive to the comparison means for preventing the allocation of the traffic channel if the number of traffic channels in use exceeds the maximum number and the mean value of quality is lower than the minimum value.
When a traffic channel request concerning the first base station, for example, is received in the cellular radio system of the invention, information is obtained about the traffic situation of the base station concerned and also the situation of the base stations located in the vicinity and using the same frequency channels. The base stations to be taken into account are preferably designated in advance, for example, a base station controller of the system can have a list stored in the memory comprising the base stations the situation of which is to be taken into account when a traffic channel is to be allocated at a particular base station. In other words, the operator has stored data on base stations for which the new traffic channel to be allocated may be significant in advance into the memory. The allocation of the traffic channel thus comprises the checking of the mean values of quality for the ongoing connections of the base stations in question. If the mean value of quality for even one base station is below the minimum quality level determined by the operator, a new traffic channel is not allocated. This ensures a high quality of the connections provided.
The invention also relates to a base station controller which can be utilized in a radio system of the invention and which is characterized in that the base station controller comprises: means for finding out the number of traffic channels in use in said radio cell; memory means into which are stored data needed for identifying adjacent cells of said radio cell; means for finding out the mean values of quality for the ongoing traffic connections of the adjacent cells; and comparison means for comparing the number of the traffic channels with a predetermined maximum number and for comparing the means values of quality with a predetermined minimum quality value; and that said allocation means are responsive to the comparison means for preventing the allocation of a traffic channel if the number of traffic channels in use exceeds the maximum number and the mean value of quality for at least one adjacent cell is lower than the minimum quality value.
The preferred embodiments of the method, cellular radio system and base station controller of the invention are disclosed in the accompanying dependent claims 2 to 4, 6.